1. Field of the Invention
The present invention relates to a differential yoke type read head and, more particularly, to first and second sensors which are located on first and second legs of a yoke at locations remote from an air bearing surface wherein the sensors have pinned layers which have magnetic moments which are 180xc2x0 out-of-phase with respect to each other.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk wherein the ABS is an exposed surface of the sensor that faces the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a tunnel junction sensor for sensing the magnetic signal fields from the rotating magnetic disk. The sensor includes an insulative tunneling or barrier layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90xc2x0 to the air bearing surface (ABS). The tunnel junction sensor is located between ferromagnetic first and second shield layers. First and second leads, which may be the first and second shield layers, are connected to the tunnel junction sensor for conducting a sense current therethrough. The sense current is conducted perpendicular to the major thin film planes (CPP) of the sensor as contrasted to a spin valve sensor where the sense current is conducted parallel to the major thin film planes (CIP) of the spin valve sensor. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is preferably parallel to the ABS, is when the sense current is conducted through the sensor without magnetic field signals from the rotating magnetic disk.
When the magnetic moments of the pinned and free layers are parallel with respect to one another the resistance of the tunnel junction sensor to the sense current (IS) is at a minimum and when their magnetic moments are antiparallel the resistance of the tunnel junction sensor to the sense current (IS) is at a maximum. Changes in resistance of the tunnel junction sensor is a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layers. When the sense current (IS) is conducted through the tunnel junction sensor resistance changes, due to signal fields from the rotating magnetic disk, cause potential changes that are detected and processed as playback signals. The sensitivity of the tunnel junction sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the tunnel junction sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the tunnel junction sensor at minimum resistance. The dr/R of a tunnel junction sensor can be on the order of 40% as compared to 10% for a spin valve sensor.
Magnetic head assemblies, wherein each magnetic head assembly includes a read head and a write head combination, are constructed in rows and columns on a wafer. After completion at the wafer level, the wafer is diced into rows of magnetic head assemblies and each row is lapped by a grinding process to lap the row to a predetermined air bearing surface (ABS). In a typical tunnel junction read head all of the layers are exposed at the ABS, namely first edges of each of the first shield layer, the seed layer, the free layer, the barrier layer, the pinned layer, the pinning layer and the second shield layer. The second edges of these layers are recessed in the head. The barrier layer is a very thin layer, on the order of 20 xc3x85, which places the free and pinned layers very close to one another at the ABS. When a row of tunnel junction head assemblies is lapped there is a high risk of magnetic material from the free and pinned layers being smeared across the ABS to cause a short therebetween. When a row of spin valve head assemblies is lapped there is a high risk of magnetic material being smeared between the shield layers and either or both of the free and pinned layers. The risk of shorting, however, is higher with the tunnel junction read head since the sense current is conducted perpendicular to the layers instead of parallel to the layers. Accordingly, there is a strong-felt need to construct magnetic head assemblies, whether they be tunnel junction type or spin valve type, without the risk of shorting between the layers at the ABS due to lapping.
The present invention minimizes shorting between the layers of either a tunnel junction type sensor or a spin valve type sensor after a magnetic head has been lapped to the ABS. This is accomplished by providing a yoke which has first and second legs which are interconnected at a location within the head at a distance d1 from the ABS wherein the first and second legs have first and second edges respectively which are located at the ABS and spaced apart by a distance d2 and wherein the first and second legs have first and second separations respectively which are located between the ABS and the distance d1 with the first and second separations magnetically disconnecting leg portions of each leg of the yoke. A first sensor is magnetically connected to the first leg across the first separation and a second sensor is connected to the second leg across the second separation. The first sensor has a first pinned layer structure and the second sensor has a second pinned layer structure wherein the first and second pinned layer structures have first and second magnetic moments respectively that are antiparallel with respect to each other. The distance d2 between the end edges of the first and second legs at the ABS are equal to a distance between magnetic impressions along a track of a magnetic disk. Accordingly, as the magnetic disk is rotated with the end edges positioned over a track one end edge will receive a field signal into or out of the head and the other end edge will receive a field signal which is in an opposite direction. Each of the field signals changes a resistance of a respective sensor, which resistances are combined in a sense current circuit and processed by processing circuitry as a playback signal. Not only is the signal significantly increased as compared to a single sensor type read head, but noise in the circuit is cancelled by common mode rejection. One sensor is preferably an antiparallel (AP) pinned type spin valve sensor and the other sensor is preferably a single layer pinned type sensor. With this arrangement the pinned layer structures next to a separation layer between the pinned layer structures have magnetic moments which are antiparallel (out-of-phase with respect to each other) so that the changes in resistances of the spin valve sensors are combined in the sensor current circuit. The present invention can be employed for either horizontally recorded magnetic media or perpendicular recorded magnetic media. In a preferred embodiment each sensor is a tunnel junction type of sensor, however, each sensor may be a spin valve type sensor. In either embodiment there is less risk of smearing between the ferromagnetic layers of the sensor or between these layers and the first and second shield layers so as to minimize the risk of shorting between the layers of the read head after the read head is lapped to the ABS.
An object of the present invention is to provide a read head which has less risk of shorting between the layers after lapping the read head to the ABS.
Another object is to provide the foregoing read head with a significantly increased signal and common mode noise rejection.
A further object is to provide a magnetic disk drive with one or more of the aforementioned read heads wherein a magnetic disk in the drive has a distance between magnetic impressions along a track of the disk which is equal to a distance between end edges of the read head at the ABS for receiving field signals from the magnetic impressions.